1. Field of the Invention
This invention relates generally to terrestrial and underwater manual and robotic hyperbaric and unpressurized welding using wire fed torches such as MIG and Flux Core torches and associated wire feeder designs, and more particularly to a welding force feedback wire feed system for such applications that incorporates a sensor feedback pressure sensor which detects deflective and deformative pressures acting on the filler wire by surrounding environmental objects and prevents the filler wire from being bent if the torch is inadvertently pressed against solid objects.
2. Brief Description of the Prior Art
Heretofore, when underwater welding operations have been undertaken using divers completing manual tasks, shielded metal arc welding methods (SMAW) using stick electrodes, suitably waterproofed in solutions beforehand have been used. More recently, the introduction of Metal Inert Gas (MIG) and Flux Core wire fed torches has been undertaken with varying degrees of success employing divers for manual applications, and Remote Operated underwater Vehicles (ROV's) in robotic applications in progressively deeper and deeper water. The ability of these types of torches to automatically feed the filler wire and protect the weld pool with a flow of shielding inert gas is seen as a benefit in underwater welding operations. But the wire feed welding process suffers from several drawbacks due to the unpredictable and movable nature of the fluid medium composing the underwater environment and the inherent design of wire feed welding equipment.
In underwater manual and robotic MIG, Flux Core, and other types of wire fed welding operations such as plasma arc the requirement exists to provide a wire feed method at or near the diver or ROV because internal friction between the wire liner in the torch electrode lead and filler wire prevents the incorporation of long lengths of electrode lead, with filler wire bunching up at the drive rollers if lengths of electrode lead over 10 meters or so are incorporated. This limitation has prevented deeper underwater applications from evolving in the past because no underwater drive roller systems have evolved. The heretofore unmet need has existed for a submersible drive roller and filler wire storage system.
In addition, when divers are moving from one underwater location to another while holding the torch or while positioning themselves to begin a weld and their attention may be directed to other objects the torch is subject to unwanted contact with metal surfaces, and bending of the filler wire may result by forceful contact of the filler wire with a solid surface where it exits from the torch cup. The simple task of straightening a bent filler wire is complicated and prolonged by the unpredictable movements of the sea which tend to destabilize the diver and the fact that the diver is wearing electrically insulating gloves which are essential to the task and must be very carefully guarded if removed. The task may require valuable time while at depth under time constraints imposed by decompression schedules, and could prevent a diver from even beginning a weld if this problem takes place at an offshore location, such as an offshore oil platform where sea movements are a particular problem.
In addition, in robotic underwater applications where a robotic torch which is attached to an ROV is used for welding under adverse sea conditions the operator may not have time to move the torch away before a collision with a stationary object occurs, and may not be aware of a potential collision beforehand due to the restricted visibility of viewing through a TV camera lens. The requirement to bring an ROV up onto a support vessel to straighten a filler wire is seen as time consuming and labor intensive, making it unattractive. In nuclear power plant welding applications, the requirement to straighten the wire may not be easily achievable due to the presence of radiation in or on the ROV and welding components themselves.
For terrestrial robotic and manual applications the convenience of a bend resistant filler wire arrangement makes a torch incorporating this feature less fragile, requiring less care and attention to the way in which it is placed on a surface when set down in manual operations or when moving a robotic arm with a torch attached or incorporated. This makes it more economical to use, requiring less of the operator's time spent on wire straightening. It is seen as advantageous to be able to prevent a bent filler wire in a torch cup if uncontrolled contact occurs with a solid object by instantaneous retraction of the wire upon initial contact, thereby preventing it from bending.
In addition to the foregoing, there has been an unmet need to address a phenomenon known as "arc stray" in deeper underwater applications, and has also evidenced itself in hyperbaric, or high pressure underwater habitat welding, where the weld is completed in a dry environment in a gas or air filled structure surrounding the welding task at depth on the sea floor or on a submerged structure. Arc stray evidences itself as instabilities of the arc during the welding process, thereby preventing adequate control over the heating and metal deposition process. It is known that the addition of a high frequency signal to a DC power signal in these non-immersed, but pressurized underwater applications will help stabilize the arc, thus minimizing arc stray and improving weld penetration. However, no development or documented experimentation has been done to combine a submersible power supply, drive roller system and high frequency initiator for either wet or hyperbaric underwater welding applications. A novel system which combines high frequency arc stabilization with a submersible power unit and a submersible drive roller for MIG and Flux Core torch filler wire is hereby disclosed which improves the depth capabilities, quality and repeatability of high quality underwater welds.
In the prior art, there is little or no evidence of development of an underwater filler wire drive roller system, nor submersible welding power and high frequency systems for use with MIG or Flux Core torches.
Heusi et al, U.S. Pat. No. 4,894,512 discloses a submersible system for impressing a high frequency signal onto a welding power signal for manual diver operation wherein the welding machine is located above the water and is connected in series to an above-the-water control console which then supplies welding power to the submerged high frequency unit, thus making the welding generator structurally unsuited to be submerged. Heusi et al uses the term "immersible welding generator", suggesting either that the generator is to be immersed in the water, or that the generator is to be used in a dry environment to create power for "immersible welding". There is no teaching in the disclosure of waterproof enclosures or waterproof elements of the welding generator itself, however Heusi et al does teach a waterproof enclosure used to house the high frequency unit, leading the reader to conclude that the purpose of Heusi et al is to retain the welding machine at an above water location, rather than submergence of the welding generator for underwater welding.
In related underwater interventions this is acceptable because the depth requirements for deep diving applications is compatible with the physical and electrical constraints imposed on a welding system with comparable length leads. A diver who is doing a deep hyperbaric weld might need leads of up to 200 meters in length, which is technically feasible with the system taught by Heusi et al. Because the invention supplies direct current power to the torch, this length becomes critical for many recent deeper ROV related robotic welding requirements which have developed in the last 4 years. More than several offshore oil industry subsea completions which have had a requirement for underwater welding have been successfully completed in water depths exceeding 1200 meters in water depth with many more in the planning stages for depths exceeding 2000 meters. Because the structural design of Heusi et al is limited to shallower depths, it would not be suitable for use in robotic applications and ROVs or other robotic vehicles.
The employment and use of DC current as the primary power source from the surface to the subsea task also makes the system taught by Heusi et al unsuitable for use in deep robotic underwater welding due to the limits of direct current, which if used would dictate very large cable diameters to compensate for high resistance losses in long cable lengths. The use of 2 very large diameter cables, on the order of 5 cm each, makes this system functionally unfeasible for even the largest work class ROV to transport to an underwater location and remain stable at great depth. The weight alone of such large cables could not be compensated for by buoyancy packaging or wrapping without making each cable over 10 cm in diameter, which is impossible for current state of the art ROVs to handle in open ocean conditions in addition to the normal control umbilical for the vehicle. In addition, Heusi et al does not teach arc stabilization in hyperbaric, or "dry" underwater welding applications where the arc does not travel through a fluid medium. The fact that high frequency arc starters and stabilizers are only commonly used in industry for Tungsten Inert Gas welding (TIG) in terrestrial applications, which have a non-consumable electrode and are not wire fed, suggests that there is not a terrestrial or shallow water hyperbaric applications problem with arc stray in combination with wire fed torches. Heusi et al's system requires that the arc is to be constantly submerged in water during the entire weld, for which SMAW underwater electrodes are designed, but MIG torches and electrodes are not. Since MIG torches have a torch cup with a shielding gas flow around the filler wire which prevents the arc from coming in contact with sea water by constantly flooding the weld area with a gas, creating a miniature gas filled hyperbaric environment around the filler wire, arc and weld pool, the Heusi et al system would also be unsuitable for use with MIG torches.
The present invention provides a method of providing welding power at extreme water depths for robotic welding applications such as MIG and deep hyperbaric SMAW welds, without requiring large umbilicals and limits the extent of arc stray displayed during diver and ROV supported underwater MIG welds.
Niinivaara, U.S. Pat. No. 4,790,887 discloses an underwater additive for underwater arc welding which is smeared on an area to be welded prior to task initiation, but does suggest the use of underwater wire feeders or drive roller systems for MIG or Flux Core torches.
Stiles et al, U.S. Pat. No. 4,654,500 discloses the use of an underwater welding housing that has a TIG torch, which has a non-consumable electrode protruding through the side of the housing into the interior, and having a sponge rubber base for evacuating water from around a weld. Stiles et al teaches the use of a TIG torch with a non-consumable torch electrode as the preferred embodiment, but there is no suggestion of the use of wire fed torches nor associated wire feed roller systems.
Asonen, U.S. Pat. No. 4,527,046 discloses an electrode which is ignitable underwater that is placed adjacent a joint to be welded and covered with a burnable shield, but does not suggest the use of a filler wire with attendant drive roller systems for the weld.
Schloerb et al, U.S. Pat. No. 4,475,026 discloses an arc stud welding system for underwater use which welds a stud as the electrode onto a metallic substrate, but does not suggest the use a drive roll system for feeding filler wire into a weld.
Johnson et al, U.S. Pat. No. 4,361,746 discloses an underwater cutting and welding torch which is adapted for SMAW welding and underwater oxy-arc cutting, but does not employ or connect to any type of drive roll system.
Stingelin et al, U.S. Pat. No. 4,172,974 discloses an underwater welding chamber which has a vortex producing swirl chamber for spinning water, the centrifugal movement producing an air filled space in the interior of the chamber which is used for welding, and which uses MIG or TIG torches, but which does not suggest a drive roller system.
None of the foregoing patents and other known prior art teaches a submersible drive roller system for use in conjunction with a MIG or Flux Core torch, and there still exists an unmet need in this industry to enable this technology so that it can provide a robotic solution to needs which require a continuously fed wire at the weld, and to enhance the productivity of manual operations involving divers at shallower depths.
In addition, there is a growing need for an enclosure to enclose submerged elements for advanced welding systems such as laser emitters, microwave emitters, homopolar generators, storage capacitors, and plasma welding and thermal spraying powder feeders, particularly in deep robotic applications.
The present invention is distinguished over the prior art in general, and these patents in particular by a MIG and Flux Core wire feed and containment system for filler wire distribution for both manual and robotic underwater and terrestrial welding applications that has a sensor feedback pressure sensor system which detects deflective and deformative pressures acting on the filler wire by surrounding environmental objects that the operator may not be aware of and which prevents the filler wire from being bent if the welding torch is inadvertently pressed against solid objects in robotic applications, thereby eliminating the need to manually straighten the wire, and enabling the capability of providing a filler wire distribution assembly at great water depths or at locations distant from the welding controls and in close proximity to the torch head.